the ground noise really bugs me...even it gets lower after warm up for like 1 hour. I think tube amp isn't the best for lazy guy like me who likes to keep things simple. I do think the taste of tube is warm and smooth, but again the noise is the part I cannot take. I guess is because both headphones I have :k702, pro900 are low resistance...too bad I sold my dt880/600 ohm and hd650 already. Otherwise I would have a chance to test if that's true.